Transmission-equalization arrangement



A. U. HARPER. TRANSMISSION EQUALIZATION ARRANGEMENT.

APPLICATION FILED OCT.2I 1919.

1,407,028, Patented Feb. 21, 1922.

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BY Hfiarper ATTORNEY 50 are undesirable. y In view of the conditions above referred ED STATES PATENT OFFICE.

ALFRED U. HARPER, QF EVANSTON, ILLINOIS. ASSIGNOR T AMERICAN TELEPHONE AND TELEGRAPH EOMPAINY, A CORPORATION OF NEW YORK.

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Application area- October 22,1919; se m n eansso.

To all whom it may concern.

siding at Evanston, in the county of Cook and State of Illinois, have invented certain llmprovements in Transmission-Equalization Arrangements, of which the following is a specification.

This invention relates to telephone systems and more particularly to the provision ofmeans for automatically obtaining a predetermined current flow ton subscribers telephone lines, irrespective of the line resistance, and thus to obtain approximately uniform transmission over such-lines.

electrical characteristics varying with the lengths of the lines. of line construction which may be employed the resistance, capacity, inductance and leakage of the circuit increasewith the length;

These variations in the electrical characteristics ofthe difierent subscribers lines in a telephone system introduce a number of variable effects in the telephone service rendered from .difl'erent stations. For example, the different electrical characteristics result in different degrees of attenuation=in the alternating telephone current passing over the subscribers lines and thus give louder and more efiective telephonic communication to subscribers connected by means of short lines than to subscribers connected byumeans of long lines. As a result, a subscriber hav-. ing' a long line, when connected with any other subscriber,'doesl not receive as good telephone transmission as would asubscriber having a short -line similarly connected. Furthermore, in the common battery systems now so generally employed in all but small 40' communities, the resistance of the line causes a further effect on the transmission in that it reduces the amount of direct current which the transmitter receives from the central ,"oflice battery and so renders it less eflicient as in the generation of the alternating telephone current. terns employing electromagnetic receivers this variation in current supply introduces changesin the efficiency of the IQOGlVQILWlHCh to, it has not been heretofore possible to provide all subscribers with the same grade of transmission and it'is one of the objects of at this invention to provide means whereby this Telephone lines have, in general, different.

For any particular type Likewise in common battery sys- I difliculty may be overcome and transmission Be 1t known that l, ALFRED U. HARPER, re-

over difierent line's equalized. @ther and further features of the invention will appear from the description hereinafter given.

lnthearrangements ofthis invention the transmlsslon equahzmg means are associated with the cord c rcuits by wh1ch connections are established with the lines, rather than with the lines themselves as in former arrangements. The talking current for the connection is'applied to the talking conductors. of the cord circuit from a battery connected with one terminal of a rheostat and after passing through a part of the rheostat the current is transmitted about the windin'gs of a plurality of relays. One of these relays .is marginal and adjusted'to operate only with current of a predetermined value Specification of Letterslatent. Patented Fb. 21, 11922.

and of a value desirable for transmission through the telephone apparatus at the subscribers sub-station. The other relay will operate on currents of very low values and controls'means for starting the rheostat in operation.- The rheostat is normally set at maximum resistance, and when a connection is made with a subscribers line by the cord circuit the low resistance relay operates to set the rheostat mechanism 1n operation. The rheostat .mechanism will continue to "operate and thus gradually decrease the rementioned predetermined desirable value,

at which point the marginal relay will operate and stop the rheostat mechanism from operating further. Additional means are provided, controlled by the marginal relay,

for locking the rheostat in position at this point. With this arrangement approx-- imately uniform transmission over subscribers lines of differing electrical characteristics may be obtained and, -furthermore, the current supplied to the telephone apparatus at the .sub-statlons may be, regulated to any desired value.

The invention may be more fully understood from the following description when taken in connection with theaccompanying drawing, in the Figures 1, 2 and 3 of which are illustrated circuit diagrams embodying a preferred form and modifications of the invention Similar reference numerals have been used to denote like parts in the figures of the invention. t

In the arrangement illustrated in Fig. 1

is shown a portion of a cord circuit terminating in the plug P and adapted for establishing connections with subscribers lines, such as the line L terminating in the jack J. Only a portion of the cord, circuit essential iion the arrangements of this invention has been illustrated, as thecord circuit may be one of many types of cord circuits well known in the art. Furthermore, only a portion of the line L has been illustrated, as the arrangements of the invention are adapted for use with lines of different types and differing electrical characteristics. 1 The talking current for a connection is supplied from the battery'B, connected to the contact 7 of rheostat mechanism 6. The rheostat mechanism 6 is held at maximum resistance by the retractile spring 8. Included in the current supply circuit is arelay 3 which operates with currents of very low value. Controlled by the relay 3 is the relay 4 which controls the clutch mechanism 9. The clutch mechanism 9 is associated withthe contact 7 of the rheostat. Contact 7 is associated with a continuously revolving shaft and motor (not shown), and the clutch mechanism 9 when operated serves to so connect the contact 7 with the revolving shaft that the contact 7 will rotate and decrease the resistance of the rheostat. Included in the talking circuit is the marginal relay 2 which is adjusted to operate on currents of a predetermined value. Marginal relay 2 exercises secondary control over relay 4 and rheostat 6 and, furthermore, controls the relay 5 whereby the rheostat may be locked in position upon the operation of relay 2. Supervisory relay. 16 and a sleeverelay 18 are shown which control the supervisory signal 17 in the usual well known manner.

The operation of the arrangements illustrated in Fig. 1 is as follows: To establish a connection with a line such as line L, the plug P is inserted in the jack J. The talking current for such a connection will be supplied over the following circuit: from ground, battery B, contact 7, resistance of rheostat 6, conductor 10, conductor 11, winding of relay 3, conductor 12, winding of mar-' ginal relay 2 conductor 13, ring conductor of cord 1, ring contacts of plug P and jack. J, ring conductor of.line L, through the'teler phone apparatus at the subscribers, substation on the line L, tip conductor of line L, tip contacts of jack J and plug P, tip

conductor of cord 1, to ground. As has been formerly pointed out, when this circuit is completed the rheostat 6 is set atmaximum resistance by means of the retractile spring 8, and accordingly the talking current supplied over the circuit will be of small value. However, the relay 3 will be operated and the following circuit closed: from ground,

contact and armature of relay 2, conductor 14, contact and armature of relay 3, winding of relay 4, to battery and ground. This will operate relay 1, which in turn will operate the clutch mechanism 9 and cause the contact 7 to rotate, thereby gradually decreasing the resistance of rheostat 6 and increasing the flow of'current over the talking circuit.

When the resistance of the rheostat has been sufliciently reduced so that the current flow over the talking circuit has reached a predetermined desirable value, the marginal relay 2 which is adjusted to operate with current of this value will operate and open at its lower contact the previously traced circuit about the winding of relay4, thereby stopping the rheostat from operat ing further. At the same time the operation of relay 2 will close the following circuit: from ground, upper contact and armature of relay 2, conductor 15, winding of relay 5, to battery and ground. The closing of this circuit will operate relay 5, which will lock the rheostat mechanism in the condition in which it was when the relay v2 was operated. No matter how the resistance or electrical characteristics of the lines with which connections are made may differ, if the relay 2 is adjusted to operate only when currents of a predetermined and desirable value are flowing over such lines, the ardown in order to signal the operator, there might be a tendency for the circuit arrangements described to be restored to normal, and, accordingly, to obviate this difiiculty the marginal relay 2 is made slow releasing.

In the arrangement illustrated in Fig. 2 is 'shown an arrangement of the invention which is substantially the same as the arrangement illustrated in Fig. 1, with the exception that an additional marginal relay 21 is included in the talking circuit for the folloyving purposes: If a connection had been established with a party line with which, are associated a number of subscribers, and if, when one subscriber had answered and the mechanism had automatically operated until .the desired talking current was being supplied to the subscriber, another subscriber should remove lllS receiver from the switch .hook, the additional resistance of the second SIIbSCIIbGI S receiver connected in parallel With the first subscribers receiver would reduce 'the total resistance of the line, and a greater-current than desired would flow over the line. Accordingly the relay 21 1s included in the talking circuit and is adjusted relays 30 and 31 will not be operated.

to operate with currents of slightly greater value than the operating currents for the marginal relay 2. Accordingly when both subscribers receivers were {removed from their respective switch hooks and a greater current than desired was flowing over the talking circuit, the relay 21 would operate. This will open the following circuit-which was closed upon the operation of relay 2: from ground, upper contact and armature of relay 2, conductor 19, armature and contact of relay 2]., conductor 15, winding of relay 5, to battery and ground. The opening of this circuit will deenergize the locking relay 5 and allow the retractile spring 8 to restore the rheostat mechanism 6 to maximum resistance thereby deenergizing relay 2. The apparatus will now .begln to function again in a normal manner as formerly described, and will regulate the current flow over the talking circuit to the desired value under the new conditions.

in Fig. 3 is a further modification of the invention in which the marginal relays and 31, which are included in the talking circuit and adjusted to operate with currents of diflerent values, serve to control the voltage at the source of current supply and thereby regulate the current transmitted through the sub-stations. If the plug P of the cord circuit illustrated in Fig. 3 is inserted in the jack J of a line of relatively high resistance and one with which it is accordingly desirable to furnish a relatively large supply of talking current, the talking circuit will be completed over the following circuit; from ground, upper right hand winding of transformer 40, tip conductor of the cord and right hand winding of marginal relay 31, ti conductor of the cord, tip contacts of plug and jack J, tip conductor of the line and through the sub-station ,apparatus associated therewith, ring conductor of the line, ring contacts of jack J and plug P, ring conductor of the cord, right han winding of marginal relay 30, ring conductor of the cord, lower right hand winding of transformer 40, conductor 36, armature and contact of relay 33, conductor 37 and through battery B, to ground. As the resistance of the line with which the connection is made is relatively high, the mar inal owever, if a connection should be made with a line of lower resistance, the marginal relay 30 would be operated and be locked up over its left hand contact and armature. The operation of marginal relay 30 will close the following circuit; from ground, right hand contact and armature of relay 30, conductor 35, winding of relay 33, to battery and ground. This will operate relay 33. Upon the operation of relay 33 the talking circuit for the connection will be completed from the lower right hand winding of transformer 40, over conductor 36, armature and make contact of relay 33, conductor 41, armature and normal contact of relay 32, conductor 38 and through a smaller portion of the battery B to ground. Accordingly a decrease in the resistance of the line with which'a connection is made will automatically cause a reduction in the amount of current supplied for the talking circuit and will thereby equalize transmission. If a connection is made with a line of still smaller resistance than in the two previous instances, the larger current transmitted over the talking circuit will cause the operation of marginal relay 31 as well as marginal relay 30, the marginal relay- 31 being adjusted to operate with currents of greater value than marginal relay 30. Upon the operation of marginal relays 30 and 31 the talking circuit for the'connection will be completed from the lower right hand Winding of transformer 40, over conductor 36, armature and contact of relay 33, conductor 41, armature and contact of rela 32, conductor 39 and through a still sma ler portion of battery 13 toground. Accordingly a further decrease in the resistance of the line with which a connection is made will cause a still further decrease inthe amountof current supplied for the connection and will thereb tend to equalize the transmission. The relays 32 and 33 are made slow releasing so that the voltage regulating apparatus will not be restored to normal every time the subscriber moves the switchhook up and down while signaling the op erator.

While it has been deemed desirable to illustrate the arrangements of the invention as included in a portion of a cord circuit, the arrangements may equally well be employed in other connecting means or connecting circuits such as trunk lines, or district or incoming selectors in automatic telephone systems. Accordingly, while the arrangements of theinvention have been disclosed in certain specific arrangements which are deemed desirable, it. is understood that they are capable of embodiment in many and widely varied forms without departing from the spirit of the invention as defined in the appended claims.

What .is claimed is:

1. In a telephone system, subscribers telephone lines of differing electrical characteristics, a cord circuit adapted to be connected with said lines, resistance varying means in the current supply circuit of said cord circuit, and a marginal relay included in the current supply circuit of said cord circuit, said marginal relay controlling said resistance varying means and being adjusted to operate with current of a predetermined value.

2. In a telephone system, subscribers telephone lines or diifering electrical. fillftllfijer circuit exercising primary control over said resistance varying means, and a marginal relay in said current supply circuit exercising secondary control over said resistance varying means and being adjusted to operate with current of a predetermined value.

3. In a telephone system, subscribers telephone lines of differing electrical characteristics, a cord circuit for establishing connections with said lines, a rheostat normally set at maximum resistance included in the current suppl circuit of said cord circuit, a relay in said current supply circuit and normally operating when said rheostat is set at maximum resistance, means controlled by said relay for decreasing'the resistance of said rheostat, and a marginal relay in said current supply circuit controllin said last mentioned means and being a justed to operate with current of a predetermined value.

4%. In a telephone system, subscribers telephone lines of diiiering electrical characteristics, a cord circuit for establishing connections with said lines, a rheostat included in the current supply circuit ofsaid cord circuit, means for normally maintaining said rheostat at maximum resistance, a relay in said current supply circuit normally operating when said rheostat is set at maximum resistance and said. cord is connected with one of said lines, means controlled by said relay for decreasing the resistance of said rheostat, a marginal relay in said current supply circuit controllin said last mentioned means and being adjusted to operate with current of a predetermined value, and means controlled by said marginal relay for locking said rheostat in an operated position.

5. In a telephone system, subscribers tele phone lines of difi'ering electrical characteristics, a cord circuit for establishing connections with said lines, a rheostat normally set at maximum resistance included in the current supply circuit of said cord circuit, a relay in said current supply circuit normally operating when said rheostat is set at maximum resistance and said cord is connected with one of said lines, means controlled by said relay for decreasing the resistance of said rheostat, and a marginal relay in said current supply circuit controlling said last 'mentioned means, said marginal relay being adjusted to operate with current of a predetermined value and being slow releasing.

6. In a telephone system, subscribers telephone lines of difiering electrical characteristics, a connecting circuit for establishing connections with said lines, a resistance varying mechanism normally set at maximum resistance included in the talking circuit of said connecting circuit, a relay in said talking circuit operating with currents of low value to start said resistance varying mechanism in operation, a second relay in said talking circuit operating with currents of a predetermined and greater value than the operating currents of said first relay, and means controlled by said second relay for stopping the operation of said resistance varying mechanism.

7. In a telephone system, subscribers telephone lines of differing electrical characteristics, a connecting circuit for establishing connections with said lines, a resistance varying mechanism normally set at maximum resistance included in the talking circuit of said connecting circuit, a relay in said talking circuit operating with currents of low value to start said resistance varying mechanism in operation, a second relay in said talking circuit operating with currents of a. predetermined "and greater value than the operating currents of said first relay, means controlled by said second relay for stopping the operation of said resistance varyingmechanism and for locking said resistance varying mechanism in operated position, a third relay in said talking circuit operating with currents of greater value than the operating currents of said second .marginal relay included in the talking circuit of said cord and controlling said cur-' rent varying means.

9. In a telephone system, subscribers telephone lines of differing electrical charae teristics, a connecting means for establishing connections with said lines, resistance varying means in the talking circuit of said connecting means, a relay in" said talking circuit exercising primary control over said resistance varying means, and a marginal relay in said talking circuit exercising secondary control over said resistance varying means and being adjusted to operate with current of a predetermined value.

In testimony whereof, I, have signed my name to this specification this 26th day of September 1919.

ALFRED U. HARPER. 

